The present invention relates to an arrangement to provide an accurate time-of-arrival indication for a received signal in communication, navigation and identification systems and the like.
Modern communication, navigation and identification systems often require accurate time-of-arrival (TOA) measurements of a received signal. One possible receiver construction is based on the use of a matched filter whose impulse response is the time-reversed signal waveform with an appropriate delay. The matched filter acts as a signal correlator and serves to detect the received signal and to estimate the instant in time when the received signal appears to be best aligned with the stored finite-duration matched waveform.
Possible approaches of the implementation of the correlator may be by utilizing a continuous-time device, such as surface-acoustic wave (SAW) devices or a descrete-time device, such as a charged-couple-device and digital correlator. The discrete-time implementation of the signal correlator is very attractive in certain application areas where module size, cost and construction flexibility and expandability are of concern. The associated sampling losses for a discrete-time system can be classified into two areas:
(1) Sampling Signal Loss--The received signal may not be sampled at the time instant that the signal-to-noise ratio (instantaneous) is locally maximum due to the timing uncertainty. PA1 (2) TOA Measurement Error--The accuracy of the TOA measurement is limited by the sampling rate (1/T) directly, i.e., the maximum TOA measurement error of .+-.T/2 may occur under a single pulse observation, where T is the sampling clock time spacing.
These two associated losses may be reduced by increasing the sampling rate for better timing resolutions at the cost of circuitry complexity.
In systems using digital correlators for the TOA measurement or indication, the accuracy of the indication is a direct function of the clocking rate, the higher the rate the higher the accuracy. The accuracy is limited by the clock rate of the correlator.